Introduction

Transcranial Doppler (TCD) is a useful tool for assessment of cerebrovascular reserve capacity in patients with high grade stenoses and occlusions of the internal carotid artery. Through measurement of cerebral vasoreactiviy, TCD may help identify patients with inadequate collateralization and increased risk of hemodynamic stroke who may benefit from surgical procedures. This chapter reviews the pathophysiologic basis of cerebral vasoreactivity and describes different techniques for its measurement with TCD. It provides an appraisal of the advantages and limitations of TCD methods as compared to other techniques for measurement of cerebrovascular reserve, and summarizes the implications of results on studies of cerebral vasoreactivity for treatment strategies in patients with carotid stenoses and occlusions.

Regulation of cerebral hemodynamics

The metabolic function of the human brain is protected by two hemodynamic mechanisms:

1. (i) Cerebral autoregulation enables constant cerebral blood flow (CBF) maintenance over a wide range of systemic blood pressure by varying the diameter of the intracerebral arterioles (Harper & Glass, 1965). This mechanism is also used to compensate for insufficiently collateralized internal carotid artery (ICA) stenoses and occlusions by lowering the peripheral vascular resistance. Maximal dilatation of the intracerebral arterioles, however, leads to decreased cerebral perfusion pressure and a corresponding reduction in CBF (Fig. 23.1).

2. […]